Thermodynamics Test

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Thermodynamics Test - 26

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Question 1
1 / -0

The statement "It is impossible to construct a heat engine which can convert heat directly to work completely" was given by

A
Clausius

B
Carnot

C
Plank

D
Kelvin & Plank

Solution

The second law of thermodynamics states , that it is impossible to construct a heat engine , operating in cycle , which extracts heat and can convert it all to useful work .In other words , it is impossible for a heat engine to convert heat completely in work .This statement is given by Kelvin & Plank .
Question 2
1 / -0

$$C_v$$ for ammonia gas is $$(in J \ mol^{-1} \ K^{-1})$$

A
$$29.0$$

B
$$12.5$$

C
$$20.7$$

D
$$31.2$$

Solution

Heat capacity of ammonia at constant volume is $$29J mol^{-1}K^{-1}$$
Question 3
1 / -0

Which statement is true for second law of thermodynamics ?

A
Heat can flow spontaneously from a cold object to a hot object.

B
You can not create a heat engine which extracts heat and converts it all to useful work.

C
According to Plank-Kelvin's law under some circumstances a perfect heat engine is possible.

D
None of these.

Solution

The second law of thermodynamics states , that it is impossible to construct a heat engine , operating in cycle , which extracts heat and can convert it all to useful work .In other words , it is impossible for a heat engine to convert heat completely in work .
The efficiency of a heat engine is ,
$$\eta=1-\frac{Q_{2}}{Q_{1}}$$
if $$Q_{2}=0$$ i.e. heat is not given to sink , it means total heat absorbed is converted into work , then
$$\eta=1$$ , which is practically not possible .
Question 4
1 / -0

A heat engine absorbs $$Q_1$$ heat from hot reservoir and work produced by engine is $$W$$, then:

A
$$Q_1$$ is always $$= W$$

B
only in some special cases $$Q_1 = W$$ otherwise $$Q_1$$ is greater than $$W$$

C
$$Q_1$$ is always less than $$W$$

D
$$Q_1$$ is always greater than $$W$$

Solution

In a heat engine , if $$Q_{1}$$ is the heat absorbed from reservoir , $$W$$ be the work done by engine and let $$Q_{2}$$ be the heat given to sink , then by the first law of thermodynamics
$$Q_{1}-Q_{2}=W$$ (internal energy$$dU=0$$ for cyclic process)
this equation gives that $$Q_{1}$$ is always greater than $$W$$ .
Question 5
1 / -0

Resistivity is

A
an extensive property

B
intensive property

C
elastic property

D
none of the above

Solution

Intensive property is a bulk property, that does not depend on the system size or the amount of material in the system. Resistivity is an intrinsic property that signifies how efficiently a given material opposes the flow of electric current. To remove the effect of size from resistance, resistivity is used - this is a material property which does not depend on size. Thus resistivity is an intensive property.
Question 6
1 / -0

What function does a Condenser perform,in heat pumps?

A
Condenser performs the most important function of cooling the room.

B
Condenser performs the most important function of heating the room.

C
Condenser performs the most important function of freezing outside the room

D
Condenser performs the most important function of heating the atmosphere

Solution

A heat pump is a device that transfers heat energy from a source of heat to what is called a "heat sink". Heat pumps move thermal energy in the opposite direction of spontaneous heat transfer, by absorbing heat from a cold space and releasing it to a warmer one. A heat pump uses a small amount of external power to accomplish the work of transferring energy from the heat source to the heat sink. A condenser is a device or unit used to condense a substance from its gaseous to its liquid state, by cooling it.

The function does a Condenser perform,in heat pumps is condenser performs the most important function of heating the room.
Question 7
1 / -0

What is the function of the evaporator in a refrigerator?

A
The evaporator supplies the heat to the substance, which is to be cooled.

B
The evaporator absorbs the heat from the atmosphere.

C
The evaporator absorbs the heat from the substance, which is to be cooled.

D
Both a and b

Solution

Evaporator is an important component together with other major components in a refrigeration system such as compressor, condenser and expansion device. The reason for refrigeration is to remove heat from air, water or other substance.

It is here that the liquid refrigerant is expanded and evaporated. It acts as a heat exchanger that transfers heat from the substance being cooled to a boiling temperature.
Question 8
1 / -0

The heat pump is also called as the :

A
Reverse motor

B
Reverse refrigerator

C
Reverse oscillator

D
Reverse engine

Solution

Though the working principle of refrigerator and heat pump is same but heat pump is used to warm a room whereas refrigerator is used to cool down the temperature of material inside it , so heat pump is also called a reverse refrigerator .
Question 9
1 / -0

What function is performed by Condenser in a refrigerator?

A
To deliver the heat to the heat pump

B
To deliver the heat to the evaporator

C
To deliver the heat to the refrigerator

D
To deliver the heat to the atmosphere

Solution

A condenser is simply a heat exchanger,the purpose of a condenser in the cycle of compression refrigeration is to change the hot gas being discharged from the compressor to a liquid prepared for use in the evaporator. The condenser accomplishes this action by the removal of sufficient heat from the hot gas, to ensure its condensation at the pressure available in the condenser. The heat is shifted to another medium, like water or air, to cool the condenser.
The function is performed by Condenser in a refrigerator to deliver the heat to the atmosphere
Question 10
1 / -0

What is most commonly used as the refrigerant in heat pumps?

A
Chlorofluorohydrocarbons

B
Fluorine gas

C
Hydrogen gas

D
Carbon gas

Solution

A refrigerant is generally a fluid , which undergoes state change , from liquid to gas and back again . Chlorofluorohydrocarbons are most commonly used as refrigerant in heat pumps .

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Thermodynamics Test - 26

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Thermodynamics Test - 26

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SHARING IS CARING

Question 1

Clausius

Carnot

Plank

Kelvin & Plank

Solution

Question 2

$$29.0$$

$$12.5$$

$$20.7$$

$$31.2$$

Solution

Question 3

Heat can flow spontaneously from a cold object to a hot object.

You can not create a heat engine which extracts heat and converts it all to useful work.

According to Plank-Kelvin's law under some circumstances a perfect heat engine is possible.

None of these.

Solution

Question 4

$$Q_1$$ is always $$= W$$

only in some special cases $$Q_1 = W$$ otherwise $$Q_1$$ is greater than $$W$$

$$Q_1$$ is always less than $$W$$

$$Q_1$$ is always greater than $$W$$

Solution

Question 5

an extensive property

intensive property

elastic property

none of the above

Solution

Question 6

Condenser performs the most important function of cooling the room.

Condenser performs the most important function of heating the room.

Condenser performs the most important function of freezing outside the room

Condenser performs the most important function of heating the atmosphere

Solution

Question 7

The evaporator supplies the heat to the substance, which is to be cooled.

The evaporator absorbs the heat from the atmosphere.

The evaporator absorbs the heat from the substance, which is to be cooled.

Both a and b

Solution

Question 8

Reverse motor

Reverse refrigerator

Reverse oscillator

Reverse engine

Solution

Question 9

To deliver the heat to the heat pump

To deliver the heat to the evaporator

To deliver the heat to the refrigerator

To deliver the heat to the atmosphere

Solution

Question 10

Chlorofluorohydrocarbons

Fluorine gas

Hydrogen gas

Carbon gas

Solution

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